This invention relates generally to the production of fluids from subterranean wells. More specifically, this invention relates to a method and to a system for producing fluids from subterranean wells using downhole fluid separation and chemical injection in combination.
Oil wells and gas wells are used to obtain production fluids from earth formations such as geological reservoirs. Production fluids from these wells consist of hydrocarbons and water. For example, a typical production fluid contains about 2%-20% hydrocarbons, and about 80%-98% water. Once the production fluid is produced to the surface, the hydrocarbons are separated from the water using well known techniques, and marketed as a xe2x80x9cproduced fluidxe2x80x9d. The separated water is referred to as a xe2x80x9cproduced waterxe2x80x9d.
One technique for increasing productivity in a well involves separating the hydrocarbons and the water in the well using a downhole separation system. For example, a separation system can include a hydrocyclone, or similar mechanical separator, for separating a well fluid into a hydrocarbon stream and water stream using fluid density differences, Rather than mechanical separation, other types of separation systems can utilize filters, membranes and electrostatic devices. Typically, the hydrocarbon stream is pumped from a producing zone of the well to the surface, and the water stream is injected into an injection zone of the well. In addition to mechanical separators, conventional downhole separation systems utilize packers to isolate the different zones, and pumps to generate the necessary fluid flow paths and pressure differentials.
The benefits accruing from downhole fluid separating techniques include reduced production costs, reduced H2S emissions, reduced scale formation, and general operational and environmental benefits from lower waste fluid volumes at the surface. In addition, the injection of water into lower reservoir zones can yield incremental production and reserves due to a xe2x80x9cwater floodxe2x80x9d response.
Another technique for increasing productivity in a subterranean well involves the injection of chemicals into the well. The chemicals can be injected into a particular zone of the well to enhance hydrocarbon recovery. A chemical injection into a producing well is sometimes termed a xe2x80x9chuff and puffxe2x80x9d due to injection of the chemical, followed by production from the well using the same well bore.
In the prior art, fluid separating techniques and chemical injection techniques have been performed separately. The present invention recognizes that fluid separating and chemical injection techniques can be used in combination for producing fluids from oil and gas wells. This results in reduced costs, reduced emissions, reduced scale formation, and increased well production.
In accordance with the present invention, a method and a system, for producing fluids in subterranean wells, are provided. The method can be performed on a conventional oil or gas production well extending from an earthen surface, into a production zone and an injection zone within the earth. In addition, the production well can include a well casing, production tubing within the well casing, and a well annulus between the production tubing and the well casing.
The method, simply stated, comprises separating hydrocarbons and water in the well, while simultaneously injecting a chemical into the well to treat selected zones of the well. A downhole separation system can be used to perform the separating step, and a chemical injection system can be used to perform the injecting step. In a first embodiment the method is performed in a well in which the production zone is above the injection zone (i.e., the production zone is closer to the surface). In a second embodiment the method is performed in a well in which the production zone is below the injection zone (i.e., the injection zone is closer to the surface).
In either embodiment, using the separation system, well fluids from the production zone of the well are downhole separated into a first stream comprising essentially hydrocarbons, and into a second stream comprising essentially water. The first stream (hydrocarbon) is pumped through the production tubing to the surface, while the second stream (water) is injected into the injection zone of the well.
For treating the well during the separation process, the chemical can be injected through the well annulus, or through a separate conduit into the selected zone. The chemical can comprise any chemical compound configured to increase the productivity of the well. Preferably the chemical has an affinity for water to permit separation from the first stream (hydrocarbon), and inclusion in the second stream (water). The first stream (hydrocarbon) which is produced to the surface, is thus essentially free of the chemical, and the second stream (water) disposes of the chemical. Representative chemicals include surfactant compounds, wettability altering compounds, and remediating compounds.
The chemical injection step can be performed one time for a time period sufficient to achieve a desired treatment of the well zone. For example, the injection step can be performed once for a selected time period, and then discontinued as separation and production of the first stream (hydrocarbon), and the second stream (water) continues. However, the injection step can also be performed continuously with the production of the separate fluids. The injection step can also be performed cyclically in an on-off sequence.
In addition to producing separate fluids, the method also chemically treats separate zones of the well. For example, the chemical can be injected into the production zone and then transported by the second stream (water) into the injection zone. Accordingly both the production zone and the injection zone are chemically treated.
The production system of the invention is configured to perform the method of the invention. The production system includes the separation system for producing the separate streams, and the injection system for injecting the chemical into the well. The separation system includes a separator apparatus in fluid communication with an injection pump, and a hydrocarbon pump which are driven by a downhole motor. The injection pump pumps well fluid from the production zone into the separator apparatus, which in the illustrative embodiment comprises one or more hydrocyclones. Using fluid density differences, the separator apparatus separates the well fluid into the first stream (hydrocarbon), and the second stream (water). The hydrocarbon pump produces the first stream (hydrocarbon) through a hydrocarbon conduit, and the production tubing to the surface. The second stream (water) is injected through a discharge tube into the injection zone.
The injection system can utilize the well annulus as a conduit for the chemical, or alternately can utilize a separate conduit placed within the well annulus to a selected zone of the well. The production system also includes devices, such as well bore packers, for isolating the different zones of the well.
In a first embodiment the production system is configured for a well in which the production zone is above the injection zone. In a second embodiment the production system is configured for a well in which the production zone is below the injection zone.